1. Field of the Invention
This invention relates generally to a waste heat recovery system on a vehicle and, more particularly, to a waste heat recovery system on a vehicle that converts engine coolant heat and engine exhaust heat to work in a Rankine cycle type heat recovery process, where the system includes valves that are selectively controlled to control whether a system fluid is first provided to a coolant heat exchanger or an economizer heat exchanger based on an exhaust heat/coolant heat power ratio.
2. Discussion of the Related Art
It is known in various industries to employ a waste heat recovery system that converts waste heat from various sources, such as an exhaust, coolant flow, etc., to a power output to provide usable work. Various types of waste heat recovery systems are known in the art. For example, a thermo-electric waste heat recovery system flows the waste heat medium over a thermo-electric material that converts the heat to electricity. Another type of waste heat recovery system employs shape memory alloys that change state or shape in response to being heated by the waste heat medium, where the change in shape is converted to work.
Another type of waste heat recovery system employs a Rankine cycle, well known to those skilled in the art, that converts heat to work by a gas expander. In a typical Rankine cycle waste heat recovery system, the system pumps a working fluid to a higher pressure and sends the high pressure fluid to a heat exchanger that receives heat from the waste heat medium, where the heated fluid changes phase from a liquid to a gas. The gas is then sent through the expander, or other device, that causes the expanding gas to perform work, such as rotating a shaft.
The automotive industry is looking into various types of waste heat recovery systems that would be compact and inexpensive enough to be suitable for a vehicle, and would efficiently convert engine exhaust and/or engine coolant heat to work to either provide additional power for operating the power train of the vehicle or provide electricity that can be stored in a vehicle battery. There is a design challenge for vehicle waste heat recovery applications to provide an efficient conversion of both the engine coolant fluid and the engine exhaust in the same waste heat recovery system for providing the work.